When the heat is too much the birds head out of town

If you have ever stood in the centre of a paved urban paradise where the buildings, roads, and parking lots add to potentially already stifling heat then you know how uncomfortable the urban heat island effect can be. Temperatures in the city, particularly densely built areas with little vegetation can increase the temperature by several degrees. This can be uncomfortable for humans, but there is a question of how it impacts other wildlife.

Cai and colleagues (2023) investigated how the urban heat island impacted bird diversity during both breeding and non breeding seasons. They weren’t surprised that bird diversity was less across all cities regardless of the city’s size or geographical location during the breeding season. What was more surprising is the birds didn’t come back to these areas during the colder non breeding season.

The researchers had hypothesized that diversity would only be reduced during breeding season. The thinking was that perhaps birds would have adapted to avoid the costs of migration and cold weather by wintering in the urban areas. This was not the case however as diversity was lower at all times.

So how do they know that this reduced diversity is from urban heat rather than just the city itself? The study looked at data from 336 Chinese cities across three time periods 2001, 2011, and 2019. Species diversity overall was significantly reduced between each period.

I would like to see this research done in other regions to see if the results hold. As well, it would be interesting to know how density and size of green spaces impacts these results. This would help improve urban planning practices. Urban heat islands are going to get worse with climate change so we need to figure out how to combat and prevent the effects.